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From page 310... ... 304 A P P E N D I X E On-Ramp Queue Spillback Analysis This document describes the methodological modifications required to address the occurrence of queue spillback from an on-ramp. The occurrence of queue spillback affects each type of intersection differently. Read the entire page →
From page 311... ... 305 Source: HCM 6th Ed. Exhibit 19-18 Figure E-1.Signalized intersections methodology with adjustments to address on-ramp queue spillback Read the entire page →
From page 312... ... 306 Step 7A - Determine intersection throughput to on-ramp The volume of vehicles that enters a freeway on-ramp is a function of the demands and capacities of each individual intersection movements that discharge into the ramp. A typical signalized intersection within a diamond interchange is shown in Figure E-2, with three movements discharging into the on-ramp (SBL, EBT and NBR) Read the entire page →
From page 313... ... 307 • Capacity of the on-ramp (Exhibit 14-12) • Capacity at the merge segment, when oversaturated conditions occur at the freeway facility • An active ramp metering RM The procedure to obtain cmerge is presented in Figure E-3. Read the entire page →
From page 314... ... 308 Figure E-3. Step 7B – Estimation of merging capacity in a freeway ramp Step 7C. Read the entire page →
From page 315... ... 309 for the SBL movement. At the end of the SBL green, the vertical difference between the projected number of vehicles (dashed line) Read the entire page →
From page 316... ... 310 Where: N(g1) = number of queued vehicles along the on-ramp at t = g1 (end of green for phase 1) Read the entire page →
From page 317... ... 311 street through or right turning traffic, but they are not required to stop in the absence of oncoming traffic. The methodologies for evaluating the operations of TWSC intersections are based on gap acceptance theory. Read the entire page →
From page 318... ... 312 Source: Adapted from HCM 6th Ed. Exhibit 20-6 Figure E-7. Read the entire page →
From page 319... ... 313 intersection into the on-ramp λONR is the sum of the throughput from each of the contributing movements. For each movement i discharging into the on-ramp, the throughput is the minimum value of its demand and its movement capacity: 𝜆 = 𝑚𝑖𝑛 𝑣 , 𝑐 , (Equation E-8) Read the entire page →
From page 320... ... 314 TSB = time period with active spillback (minutes) T = duration of analysis time period (minutes) Read the entire page →
From page 321... ... 315 The average control delay is obtained using Equation 20-64 replacing the movement capacity cm,i by the adjusted capacity cEQ,i: 𝑑 = 3600𝑐 , + 900𝑇 ⎣⎢⎢ ⎢⎡ 𝑣𝑐 , − 1 + 𝑣𝑐 , − 1 + 3600𝑐 , × 𝜆𝑐 ,450𝑇 ⎦⎥⎥ ⎥⎤ + 5 (Equation E-13) Read the entire page →
From page 322... ... 316 All-Way Stop-Controlled (AWSC) Intersections The methodology to evaluate queue spillback into AWSC intersections follows the approach developed for TWSC intersections. Read the entire page →
From page 323... ... 317 ℎ = 3600𝑐 , (Equation E-14) Roundabout ramp terminals The methodology presented in Chapter 22 – Roundabouts is shown in Figure E-10. Read the entire page →
From page 324... ... 318 Source: HCM 6th Ed. Exhibit 22-15 Figure E-10. Read the entire page →
From page 325... ... 319 Table E-1. Required data and potential data sources – roundabout spillback evaluation Required Data and Units Potential Data Source Suggested Default Onramp Data On-ramp metering rate (veh/h) Read the entire page →
From page 326... ... 320 cSB = lane capacity for SB approach (veh/h) (HCM Equation 22-21) Read the entire page →
From page 327... ... 321 the queue storage is insufficient. The analyst must then proceed to Step 17 to evaluate the onramp Queue Storage Ratio to evaluate whether spillback will occur. Read the entire page →
From page 328... ... 322 Step 19. Calculate the average control delay per approach To estimate the average delay per approach, the delay due to the on-ramp capacity limitation is estimated and added to the approach control delay calculated in Step 9 (HCM Chapter 22) Read the entire page →
From page 329... ... 323 Case Study: Evaluating Queue Spillback from Freeway On-Ramp This case study illustrates the application of the on-ramp spillback methodology by evaluating operations at an interchange when there is queue spillback originating from the on-ramp. There are three parts to the case study with each one analyzing a different intersection type at the ramp terminal: signalized, TWSC and AWSC. Read the entire page →
From page 330... ... 324 Part 1 – Signalized Intersection Input data Signalized Intersection The geometry of the intersection connected to the I-10 EB on-ramp (I-10 EB) is shown in Figure E-13. Read the entire page →
From page 331... ... 325 Table E-2. Demand flow rates (veh/h) Read the entire page →
From page 332... ... 326 Figure E-15. Freeway facility segmentation– I-10 EB The geometric features of the freeway facility are summarized in Table E-4. Read the entire page →
From page 333... ... 327 throughput of the unsignalized turning movement is also assumed to be equal to its saturation flow rate. Therefore: 𝑠 , = 𝑠 , × 𝑓 × 𝑓 where sNBR,FF = saturation flow rate of NBR movement at free-flow conditions (veh/h/ln) Read the entire page →
From page 334... ... 328 • During the queue service time (gs) portion of the conflicting phase green, the opposing movement flow rate is equal to its saturation flow rate; • During the green extension time (ge) Read the entire page →
From page 335... ... 329 Table E-7 summarizes the calculations for this step. During time period 3, the SBL movement operates at demand over capacity (v/c = 1.56) Read the entire page →
From page 336... ... 330 Table E-9. Performance measures for the freeway facility (I-10 EB) Read the entire page →
From page 337... ... 331 Oversaturated Segment Evaluation procedure (HCM Chapter 25) computes the on-ramp queue (ONRQ) Read the entire page →
From page 338... ... 332 Figure E-16. Freeway facility, segment 5 (merge) Read the entire page →
From page 339... ... 333 Step 7C – Plot queue accumulation polygon for the on-ramp and unsignalized movements In this step, a queue accumulation polygon is plotted for the on-ramp as a function of all protected and permitted movements entering the on-ramp, on a cycle-by-cycle basis. Since an unsignalized movement (NBR) Read the entire page →
From page 340... ... 334 𝑠 , = 𝜆 𝑒 / ,1 − 𝑒 / , Where: sNBR,perm = saturation flow rate of the NBR movement (veh/h/ln) λSBL = throughput of the opposing SBL movement(veh/h) Read the entire page →
From page 341... ... 335 with all variables previously defined. Since a queue is present in the NBR movement, the throughput for the NBR movement is equal to its saturation flow rate: 𝜆 , = 𝑠 , = 1282 𝑣𝑒ℎ/ℎ Where: λNBR,2 = throughput for the NBR movement during the SBL green extension(veh/h/ln) Read the entire page →
From page 342... ... 336 • ge7* Read the entire page →
From page 343... ... 337 Step 7B – Obtain merging capacity with Freeway Facilities method As in the analysis of the previous time period, the merging capacity cmerge is obtained as an output from the Freeway Facilities method (Figure E-16a) Read the entire page →
From page 345... ... 339 Table E-13. Discharge flow rates into the on-ramp for each phase throughout the cycle – time period 3 Active phase t (s) Read the entire page →
From page 346... ... 340 Table E-14. Calculation of spillback capacity reduction factor for the SBL movement for time period 3 Cycle Active phase Duration (s) Read the entire page →
From page 347... ... 341 Figure E-19. Estimated queue lengths and merge capacities – time period 4 Step 7D – Calculate adjusted capacities for the affected movements The procedure described earlier is used to calculate the capacity reduction factor for the SBL movement, as shown in Table E-15. Read the entire page →
From page 348... ... 342 6 gs1 40.2 0.00 0.561 0.561 1.000 22.55 22.55 6 ge1 3.7 1.31 0.392 0.392 1.000 1.46 1.46 7 gs1 40.2 0.00 0.561 0.561 1.000 22.55 22.55 7 ge1 3.7 1.31 0.392 0.392 1.000 1.46 1.46 8 gs1 40.2 0.00 0.561 0.561 1.000 22.55 22.55 8 ge1 3.7 1.31 0.392 0.392 1.000 1.46 1.46 Total: 170.49 164.86 Spillback capacity reduction factor: 0.967 The adjusted capacity of the SBL movement is calculated by applying the spillback capacity reduction factor βsp, calculated in Table E-15: 𝑐 , = 𝑐 × 𝛽 , = 746 × 0.967 = 𝟕𝟐𝟏.𝟒 𝐯𝐞𝐡/𝐡 With the adjusted capacity values obtained, the performance measures for the intersection can be computed using the remaining steps from the Signalized Intersections methodology (Chapter 19) : compute the adjusted demand-to-capacity ratio (Step 8) Read the entire page →
From page 349... ... 343 Figure E-20. TWSC intersection geometry – Acadian Thruway @ I-10 EB Spillback check – on-ramp The first step in the spillback check analysis is to determine the on-ramp demand flow rates for each time period, based on the demand inputs of the TWSC intersection. Read the entire page →
From page 350... ... 344 Table E-17. Calculation of the on-ramp demand (vR) Read the entire page →
From page 351... ... 345 calculated. Then, the time to spillback is obtained considering the queue growth and the available queue storage. Read the entire page →
From page 352... ... 346 The capacities during spillback conditions are then obtained proportionally to their demand flow rates (Equation E-10) : 𝑐 , = 𝑐 × 𝑣𝑣 + 𝑣 + 𝑣 = 1,142 × 685685 + 708 + 18 = 554.4 𝑣𝑒ℎ/ℎ 𝑐 , = 𝑐 × 𝑣𝑣 + 𝑣 + 𝑣 = 1,142 × 708685 + 708 + 18 = 573.0 𝑣𝑒ℎ/ℎ 𝑐 , = 𝑐 × 𝑣𝑣 + 𝑣 + 𝑣 = 1,142 × 18685 + 708 + 18 = 14.6 𝑣𝑒ℎ/ℎ The equivalent capacities cEQ,i for each movement i, aggregated for the 15-min time period, are obtained proportionately to the spillback time TSB (Equation E-11) Read the entire page →
From page 353... ... 347 Figure E-22. AWSC intersection geometry – Acadian Thruway @ I-10 EB Spillback check – on-ramp The first step in the spillback check analysis is to determine the on-ramp demand flow rates for each time period, based on the demand inputs of the AWSC intersection. Read the entire page →
From page 354... ... 348 Table E-20. Calculation of the on-ramp demand (vR) Read the entire page →
From page 355... ... 349 Step 13A - Determine intersection throughput to on-ramp The intersection throughput to the on-ramp was previously determined at the spillback check (Table E-20) Read the entire page →
From page 356... ... 350 Table E-23. Equivalent capacities and headways for on-ramp – Time Period 3 – AWSC intersection Movement Capacity during spillback (csp) Read the entire page →

From page 310...

... 304 A P P E N D I X E On-Ramp Queue Spillback Analysis This document describes the methodological modifications required to address the occurrence of queue spillback from an on-ramp. The occurrence of queue spillback affects each type of intersection differently.